The present invention relates to an apparatus for controlling the temperature of an internal combustion engine including a spark ignition engine and a diesel engine and more particularly to an apparatus which controls the engine temperature by controlling the temperature of a working fluid or fluids capable of exchanging heat with the engine.
In a spark ignition engine, the temperature of the combustion chamber walls, in general, is too low under a low load condition and this leads to incomplete combustion and provides more unburned components, such as HC and CO, in the exhaust gases. Under a high load condition, on the other hand, increasing the compression ratio to improve the fuel consumption causes an increasing knock tendency.
In a diesel engine, the ignition lag is large during idling so that what is called diesel knock is liable to occur. And since the heat load is severe under high load condition, there is a necessity for a more rigid structure of the engine which eventually makes the engine more heavy and expensive.
It is one of the major factors causing these undesired problems that the temperature of the combustion chamber walls and the temperature of the intake air are too low at low load and too high at high load.
In a conventional engine cooling system, the temperature of the cooling water to cool the combustion chamber walls is controlled constant at about 80.degree. C. Accordingly the combustion chamber walls are cooled excessively at low load while on the contrary cooling is insufficient at high load. And the engine intake air is warmed up only during a warm-up period in some cases but there has never been provided means for cooling the intake air at high load. So far there is no idea of controlling the temperature of a working fluid or fluids, such as engine intake air, engine coolant and lubricating oil, of the engine to a desired temperature varying in accordance with the engine operating conditions and therefore the undesired problems mentioned above are considered to be unavoidable.